Methods of treating metal



May 23, 1967 w. E. KNAPP ETAL METHODS OF TREATING METAL Filed NOV. 13, 1963 INVENTORS William E. Knapp 8 g Wilbur T. Bolkcom United States Patent ()flice 3,321,006 Patented May 23, 1967 3,321,006 METHODS OF TREATING METAL William E. Knapp, Allison Park, and Wilbur T. Bolkcom, Pittsburgh, Pa., assignors to American Metallurgical Products Company, a corporation of Delaware Filed Nov. 13, 1963,.Ser. No. 323,343 2 Claims. (Cl. 164-56) This invention relates to methods of treating metal and particularly to method of treating metal in the mold. The method of this invention has its greatest usefulness in the steel industry and will be described in relation to the treating of steel although the same practice can be used in the treatment of other metals in like manner.

The problem of reducing inclusions in steel and other metals has been one that has plagued the metal working industries for years. At the same time, the problem of controlling surface quality so as to produce the minimum loss in metal yield and the minimum amount of surface conditioning has been equally significant. We have discovered a method and means of treating metals to eliminate all of these problems. The practice of our invention will result in a marked reduction in inclusions resulting from gases such as oxygen and hydrogen and will produce a superior ingot surface requiring minimum conditioning.

In a preferred embodiment of our invention, we insert into a mold into which metal is to be poured, a bag made of a material containing releasable fluorine or fluorine and chlorine and of a size suflicieut when expanded to completely fill the mold and bear against the side of the mold. The bag is inserted into the mold and is preferably expanded by nitrogen, an inert gas such as argon or a gas having desirable reactive properties with the metal such as one of the hydrocarbons, e.g., propane, or a member of the halide family such as one of the Freons. When the bag has been completely expanded in the mold into contact with all of the mold surfaces, the molten metal is teemed directly into the interior of the bag. This results in fusion of the bag and reaction of the bag with the molten metal as it rises up the surface of the mold. The practice of the invention and the installation of the bag are illustrated in the accompanying figure in which a stool is provided with a mold 11 into which is placed a bag 12 according to the invention. The bag 12 is made up of a material containing releasable fluorine and/or chlorine. The bag may, for example, be made of polytetrafiuorethylene (C 1 fluorohalocarbon (C ClF or any other similar material capable of being formed into a bag which will contain the expanding gas and which will release fluorine or fluorine and chlorine under heat. The bag 12 is inserted into the mold in the collapsed condition. It is expanded in the mold into contact with the mold walls 11 and stool 10 by passing an inert gas such as nitrogen, argon or a gas having desirable reactive properties with the metal into the interior of the bag through a valve 13. The valve 13 may be a simple plastic tube which can be tied in a knot to prevent the inert gas from leaking out while the mold is awaiting teeming of the metal.

The practice of this invention provides a reaction of the bag components along the surface of the mold as the metal rises and gives surface protection and surface conditioning which cannot be attained by adding a solid gas releasing material in the conventional manner. At the same time, it provides a desirable protective gaseous atmosphere in which the metal is poured without the excessive losses customarily expected when using a purging gas in the mold prior to teeming as, for example, when purging with argon in the conventional manner. This results in the use of only about percent as much purging gas as conventional practices, while at the same ill time, providing a percent purge and 100 percent purity of atmosphere at the time teeming begins, a result impossible to achieve with conventional purging practices. Preferably, the bag is provided with one thickness along the mold walls and a multiple thickness at the bottom and top of the bag. However, this thickness differential is not essential to the practice of the invention and the bag may be uniform in thickness over its entire surface. The valve through which gas is introduced into the bag may be any of a variety of valves.

It is, of course, possible to maintain the advantage of the surface treatment without the purging action simply by inserting the bag into the mold and blowing it into contact with the side walls without the use of inert or reaction gas. For example, the bag may simply be pressed into the mold by blowing in air if it is desired only to attain the surface conditioning properties attainable by the reaction of the bag component.

The advantages of the practice of this invention are many. In addition to the reduction in ingot conditioning and ingot loss, the advantages of complete reliability of purging, of the elimination of mold washes, of the reduction in pick up of undesirable gases such as hydrogen and oxygen and the teeming at lower temperatures with good surfaces are products of this practice.

The practice of this invention can perhaps be best illustrated by the following examples:

Example I A bag made of fiuorohalocarbon was formed to fit into a mold 22 inches in diameter by inches high. The bag was inserted into the mold in the deflated condition and was inflated through a plastic hose with dry argon until a pressure several ounces above atmospheric was obtained. (This pressure is not critical. The only requirement being that it should be adequate to force the bag to conform snugly with the mold wall.) The molten steel was teemed in a conventional manner from a ladle into the plastic bag. The bag immediately began to decompose in contact with the molten metal releasing carbon in the form of lampblack, chlorine and fluorine. These released materials were sufiicient to prevent the inspiration of air into the mold with the flowing stream of steel. The steel which was used in this particular example was grade A-286. Gas evolution took place constantly as the mold filled and the bag was gradually consumed with the rising metal. The consumption of the bag provided the control of gas evolution consistent with the rate of teeming which has heretofore been unattainable in any other practice. A mold without the bag of the present invention was poured from the same melt of steel and a comparison of the ingots was made. The mold without the bag was purged by bubbling dry argon through the bare mold and fluorohalocarbon in pebble form was thrown into the mold to provide fluorine and chlorine. A comparison of the two ingots showed the following results:

The practice described in Example I using an AISI grade 321 steel and an ingot mold 25 by 27 by 74 inches high was repeated. A comparison of the follows:

results is as Arcomparison of the test results shows the marked improvement in surface condition provided by the practice of our invention. The argon required in the conventional practice was approximately three times as great as in the mold treated by our process.

While we have illustrated and described certain preferred practices and embodiments of our invention, it will be understood that this invention may be otherwise embodied within the scope of the following claims.

We claim:

1. The method of treating molten metal which comprises the steps of expanding a bag made of a material containing releasable fluorine into contact with the mold Walls, pouring molten metal into the interior of the bag to fill the mold while the action of molten metal causes release of said fluorine in amounts providing surface protection and conditioning during said pouring and solidify the metal therein.

2. The method of treating molten metal which comprises inserting a bag made of a material containing releasable fluorine into a mold, filling the bag with a gas selected from the group consisting of inert gases, nitrogen and reactive gases to expand the bag into contact with the mold walls and pouring molten metal into the interior of the bag to fill the mold while the action of molten metal causes release of said fluorine in amounts providing surface protection and conditioning during said pouring and thereafter solidifying the metal.

References Cited by the Examiner UNITED STATES PATENTS 800,213 9/1905 Jacobs 22-163 1,940,619 12/1933 Barstow et al. 75-17 2,345,977 4/1944 Howald et al. 2,499,324 2/1950 Mead 18-47 3,078,531 2/1963 Bolcom et al. 3,142,099 7/1964 Burch 22214 3,158,913 12/1964 Bolcorn et al. 22-215 I. SPENCER OVERHOLSER, Primary Examiner.

5 V. K. RISING, Assistant Examiner. 

1. THE METHOD OF TREATING MOLTEN METAL WHICH COMPRISES THE STEPS OF EXPANDING A BAG MADE OF A MATERIAL CONTAINING RELEASABLE FLUORINE INTO CONTACT WITH THE MOLD WALLS, POURING MOLTEN METAL INTO THE INTERIOR OF THE BAG TO FILL THE MOLD WHILE THE ACTION OF MOLTEN METAL CAUSES RELEASE OF SAID FLUORINE IN AMOUNTS PROVIDING SURFACE PROTECTION AND CONDITIONING DURING SAID PURING AND SOLIDIFY THE METAL THEREIN. 